Broadband circularly polarized antenna having a continuous rectangular aperture

ABSTRACT

A BROADBAND CIRCULARLY POLARIZED ANTENNA HAVING A CONTINUOUS RECTANGULAR APERTURE TO OBTAIN CIRCULAR POLARIZATION, HAVING UNIFORM PHASE AND TAPERED AMPLITUDE ILLUMINATION OVER THE BROAD DIMENSION OF THE APERTURE. THE DEVICE FEATURES A LARGER EFFECTIVE RADIATING OR RECEIVING APERTURE THAN COMPARABLE RECTANGULAR ARRAY OF CIRCULARLY POLARIZED SPIRALS DUR TO THE USE OF VIRTUALLY LOSSLESS RADIATING   ELEMENTS TO PROVIDE HIGHER GAIN. LINEARLY POLARIZED RADIATING ELEMENTS ARE UTILIZED TO FEED AN APERTURE WITH LINEARLY POLARIZED ENERGY WHICH IS THEN TRANSFORMED INTO CIRCULARLY POLARIZED ENERGY BY MEANS OF A POLARIZER GRID.

United States Patent O 3,560,984 BROADBAND CIRCULARLY POLARIZED ANTENNAHAVING A CONTINUOUS RECTANGULAR APERTURE Tsze K. Lee, New Rochelle,Arthur Winkler, Bronx, and

Wai Wong, Plainview, N.Y., assignors to Loral Corporation, Scarsdale,N.Y., a corporation of New York Filed Dec. 11, 1968, Ser. No. 783,047Int. Cl. H01g 15/24, 21/08, 13/02 U.S. Cl. 343-756 3 Claims ABSTRACT OFTHE DISCLOSURE This invention relates generally to the field ofcircularly polarized transmitting antenna particularly suited forbroadband communication or reception for ECM and other similarapplications.

It is among the principal objects of the present invention to provide animproved antenna construction in which azimuth and elevation beamwidthsmay be simply controlled by aperture size, using a single monopolearray.

Another object of the invention lies in the provision of an improvedantenna construction in which greater gain is available as compared withcomparable rectangular array spiral constructions known in the art.

A further object of the invention lies in the provision of improvedantenna construction offering shorter depth and superior apertureillumination control, as compared with conventional sectoral horn andpolarizer constructions.

Still another object of the invention lies in the provision of improvedantenna construction in which superior reproducibility and ease offabrication are realized as cornpared with rectangular array of spiralconstructions.

A feature of the disclosed embodiment lies in the fact that multiplearrays may be vertically stacked to obtain a two dimensional array,where required.

These objects and features, as well as other incidental ends andadvantages, will more fully appear in the progress of the followingdisclosure, and be pointed out in the appended claims.

In the drawing, to which reference will be made in the specification,FIG. l is a front elevational view of an embodiment of the invention.

FIG. 2 is a transverse sectional view thereof as seen from the plane 2-2in FIG. 1.

FIG. 3 is a bottom plan as seen from the plane 3 3 in FIG. l.

In accordance with the invention, the device, generally indicated byreference character 10, comprises broadly: a rectangular channel cavityelement 11, a polarizer grid element 12, and a plurality of monopoleelements 13.

The rectangular channel cavity element 11 may be of conventional sheetmetal construction, including a rear wall 15, an upper wall 16, and alower wall 17 defining a cavity area 18. Flared portions 19 and 20communicate 3,560,984 Patented Feb. 2, 1971 lCe with flange portions 21and 22, and support a strip of re` sistive card 23 through a foammaterial support 24.

The polarizer grid element 12 includes first, second and thirdphoto-etched gratings 30, 31 and 32, respectively, maintained in spaceparallel relation by a pair of dielectric spacers 33 and 34 and two edgeretaining rims 35.

The monopole elements 13 are similar, and are mounted by connectormembers 39 in front of the rear wall 15, as best seen in FIGS, 2 and 3in the drawing.

In a preferred embodiment, the channel cavity element is nine incheslong, 0.5 inch high and one inch deep. The monopoles are spaced 0.75inch on centers. The depth of the channel is extended in the forwarddirection by aring to a desired vertical aperture of 1.53 inches. Thepolarizer grid is nine inches long by 2.25 inches high by 0.5 inchthick, and serves to convert linear polarization to circularpolarization. The resistive card is placed parallel to the axis of wavepropagation, and serves to suppress unwanted orthogonal linearpolarization. The antenna pattern is nominally circularly polarized witha narrow azimuth beamwidth and a broad elevation beamwidth.

Excitation of the monopole elements is obtained through a printedcircuit feed network (not shown) of conventional type which providessymmetrically tapered amplitude illumination and uniform phase acrossthe monopole array. A hybrid input (not shown) to the feed networkprovides sum and difference radiation patterns.

A device constructed in accordance with the above description wasmeasured over a bandwidth of 1.4721 in X- band, the results beingsummarized as follows.

Gain measurements were taken at the output of the sum channel of thehybrid. The gain of the maximum polarization response at the peak of thebeam varies from 11.5 to 12 db over the band with an average value of13.5 db. Gain is referred to a linear isotrope.

The side lobe level is a function of the illumination. For the chosenillumination, the largest side lobe is 16.5 db down from the peak of thesum beam for horizontal polarization. Elsewhere over the band, the sidelobe level is generally at least 20` db down over most of the band forboth orthogonal linear polarizations.

The voltage standing wave ratio at the input to the hybrid sum channelshows a maximum ratio of 4.0:1 at one frequency near the low end of thefrequency band. Over the greater portion of the band the ratio is under2.0:1.

The axial ratio measured at the peak of the sum beam is less than 2.0 dbover most of the band except at the low end where a maximum of 3.1 db isobtained.

We wish it to be understood that we do not consider the inventionlimited to the precise details of structure shown and set forth in thisspecification, for obvious modications will occur to those skilled inthe art to which the invention pertains.

We claim:

1. A broadband circularly polarized antenna comprislng:

a rectangular channel cavity element defining an elongatedrectangularly-shaped enclosed area, a plurality of monopole elementspositioned on a wall of said cavity element in rectilinear array, saidchannel cavity having a ared portion outwardly diverging in thedirection of wave propagation, and a polarized grid element overlying anouter end of said ared portion; a resistive card disposed within saidared portion, and lying in a plane parallel to the direction of wavepropagation.

2. A broadband circularly polarized antenna comprising:

ilared portion; said grid element including a plurality of planargratings and a plurality of dielectric HERMAN KARL SAALBACH PrimaryExammer separating members disposed between said gratings. 10 M.NUSSBAUM, Assistant Examiner 3. Structure in accordance with claim 2,including a resistive card disposed Within said ared portion, and ly-U.S. C1. X.R. ing in a plane parallel to the direction of wave propaga-333 98. 343 776 `824 909 tion.

